1. Field of the Invention
The present invention is directed to; high pressure containment apparatuses; blowout preventers; to ram locking mechanisms for them; and to methods of their use.
2. Description of Related Art
In a variety of situations, blowout preventers are used to control sub-surface pressures that may adversely affect equipment used in drilling oil and gas wells. Manual mechanisms and pneumatic or hydraulic pressure are employed to act on a piston to close or open ram sealing elements. Often hydraulic actuation is used since the required closing forces are relatively high. Hydraulic actuation force is applied to a cylinder containing a piston which in turn acts on a shaft having a ram element connected thereto. In certain prior art blowout preventer systems, a ram locking member is operable by turning an exterior shaft extension projecting from the blowout preventer. Alternatively the locking member is movable automatically, e.g. using known automatic operator apparatus, e.g., but not limited to known POSLOCK™ apparatus available from National Oilwell Varco, owner of the present invention.
U.S. Pat. No. 5,575,452 co-owned with the present invention, discloses, inter alia, a blowout preventer ram actuator mechanism with a primary piston including an outer sleeve portion which supports an independently movable locking piston which has tapered surfaces, and locking segments each engage one of a plurality of tapered locking rods fixed to the actuating mechanism housing. U.S. Pat. No. 7,195,224, co-owned with the present invention, discloses, inter alia, blowout preventers having a main body, a ram system with ram apparatus, a movement system with movable shaft apparatus connected to the ram apparatus, the ram apparatus movable from a first open-ram position to a second closed-ram position, the movable shaft apparatus including a locking shaft portion having a tapered portion, a locking system for selectively locking the ram apparatus in the closed position and having locking member apparatus having a primary tapered surface in contact with the locking shaft portion which is movable with the so that the primary tapered surface contacts the tapered portion of the locking shaft portion to releasably lock the movable shaft apparatus.
In many prior ram-type blowout preventer systems, once rams have been moved to contact a tubular, e.g. a pipe, the rams are locked in place by turning a lock shaft connected to a ram shaft to which a ram is connected. Rotating the lock shaft sufficiently to lock a ram in position can often take a relatively long time.
Various prior blowout preventers have a main body with a projecting member or operating/cylinder “head” through which the lock shaft extends. External threading on the lock shaft threadedly engages internal threading on the head. Rotation of the lock shaft with respect to the head locks the ram shaft and the ram in a desired position preventing the ram from disengaging from a pipe. The head adds size and weight to the overall system and, in some cases, enlarges the distance that a lock shaft must travel to lock a ram in place. The head is designed to be sufficiently large and massive to handle the locking load, the load imposed on the ram shaft and the lock shaft by force acting on the rams pushing them out of engagement with a pipe (force from wellbore pressure active on a ram shaft or rubber pressure forcing the rams apart).
In certain prior blowout preventers in order to move a ram out of engagement with a tubular and open a bonnet or door, the bonnet must move the length of the ram plus the length of the stroke of a ram operator. In certain prior blowout preventers separate hydraulic circuits are used for ram movement and for bonnet movement.